Constant frequency circuits



30, 1932- c. D. BARBULESCO 1,874,222

CONSTANT FREQUENCY CIRCUITS Original Filed Sept. 13. 1928 Patented Aug. 30, 1932 UNITED STATES PATENT OFFICE GONSTANTIN D. BARIBULESCO, OF DAYTON, OHIO, ASSIGNOR TO PAUL S. EDWARDS, OF

I DAYTON, OHIO CONSTANT FREQUENCY CIRCUITS Application filed September 13, 1928, Serial No. 305,753. Renewed December 3, 1931.

This invention relates to constant frequency circuits and has reference more particularly to high frequency vacuum tube oscillators of the type employed for heterodyne wavemeters and other similar uses.

Prior'to this time the. difficulty which has existed in the design of a heterodyne wavemeter, when the electron tube is used as a generator, is the change in'frequency due to ly impossible to maintain the frequency of a vacuum tube oscillator within the limits required for-a good receptionofradio signals. Among the causes which produce the undesired shift in frequency I can. enumerate the fluctuations in the plate voltage and filament temperature, the changes in tube characteristics, the-swinging of the antenna, etc. If the oscillator is used as a heterodyne'wavemeter the instrument must be calibrated not only when the tube is replaced but also sev-, eral times during the normal life of the same tube. Moreover, great care should be taken in maintaining the filament temperature and the plate voltage as constant as possible.

This is a very tedious-and expensive process,

so that, in the modern practice, a Piezo electric crystal is preferred to control and maintain the frequency of vacuum tube oscillators. f

Thecrystal controlled vacuum tube oscillators are, however, expensive andflackin flexibility when the same oscillator is desired to cover a wide band of frequencies.

and having all the flexibility desired.

the variations of the filamenttemperature,

It is also well known that when using frequencies above 1000 kilocycles it is practical.

Another object of this invention is to pro-' vide a vacuum tube oscillator able to;maintain, to a high degree, .constant frequency Still another object of thisfinvention is' to devise a vacuum tube oscillator that is" and operate.

into practical efiect, without limiting the improvements in their useful application to the particular constructions, which, for the purpose of explanation, have been made the subject of illustration.

In the drawing: 1

Fig. 1 is a diagram of the preferred form of my improvedcircuit showing the several elements involve v Fig. 2 is a diagram showing the electrical equivalent of the circuit shown in Fig. 1.

Fig. 3 is a diagram of a modified form of my improved circuit wherein the grid is maintained at ground potential.

Fig. 4 is a vector analysis illustrating more clearly the theory of-the present invention.

Referring by numerals to the drawing wherein the same elements are designated by like symbols, the numerals 1, 2 and 3'designate respectively the plate, grid and filament of a vacuum tube comprising between grid and plate a specially designed oscillatingcircuit. This circuitis composed of a few turns of heavy metallic conductor, 4, and a variable condenser, 5, of unusually large value. 6 and 7 are ordinary radio frequency choke coils producing across the oscillating circuit 4-.5 a composite driving electromotive force. 8 is another radio. frequency choke which maintains the filament at higher radio frequency voltage than the filament power supply, which ordinarily has great stray capacity to ground. 9 is a grid condenser and 10 is a grid resistance or leak; these elements provide a proper bias to the grid of the tube, thus maintaining the plate current within safe limits.

11 and 12 are fixed condensers of very large value; they bypass the radio frequency current flowing in the plate circuit. It is possible, therefore, to maintain the plate and the plate power supply at ground potential with respect to the high frequency oscillations.

2 shows the electrical equivalent of the circuit and Fig. f the vector diagram of the high frequency voltages and currents flowing in it, with their respective phases.

lVhenthe tube is in oscillating condition a high frequency electromotive force E appears in the grid circuit which produces an electromotive force ,u. times greater in the plate circuit; ,a being the voltage amplification constant of the tube. A current the condenser, C, extremely large, the oscil lating currents maintained therein are very large and nearly all the oscillatmg energy 18 located in this circuit. I have demonstrated this by placing high frequency meters in different sections of the circuits and the ratio 5 I0 is found to be around 1/100 in a well designed circuit. a

I have demonstrated the novel and useful 7 features of my circuit by extensive research as follows:

1. A loop transmitter working around 3000 KC has been designed in which the number of turns in the coil has been reduced to only one loop of copper or aluminum tubing of large dimensions. The energy is thus radiated directly from the source without transfer into another circuit, which may introduce losses and complications in the behavior of the tube. transmitter remains so constant that a hand driven generator may be used to supply the power required for the filament and plate'cire On account 7 The frequency of this device the note of the signal is pure, and reliable communication can be assured at distances varying with the power of the tube.

2. When greater power is needed the circuit may be used as master oscillator driving amplifying tubes able to handle greater power. The constancy of frequency of a transmitter properly designed along these principles can compare favorably with similar devices in which the frequency is controlled by crystals and has the advantage of much greater flexibility in adjusting the frequency to any desired value.

3. As a heterodyne wavemeter the circuit has marked advantages over the crystal controlled circuits.

At 3000 kilocycles a similar device using small tubes was able to maintain the frequency within 150 cycles when several tubes, picked at random, have been interchanged and the filament current or the plate voltage Varied within 25% of their initial value.

As compared with the frequency of 3000 kilocycles the instrument is able to maintain the calibration within modified as shown in Fig. l and two radio frequency chokes 8 are needed to keep the filament 3 at higher voltage than the power V supply. The plate supply is maintained also at ground potential by locating it on the grid side as shown. The bypass condensers, 11 and 12, are located in the new positions indicated.

From the foregoing description it is apparent that I have provided a circuit in which the value of L and L can be kept high and i r I still have a very high naturalfrequency. At

the same time the value of C is great because the two coils L and L are shunted by L which has a small value of inductance.

' Therefore the frequency of my improved circuit is not far from thenatural frequency of the circuit L, O.

The symbols and nomenclature employed in this specification are standard.

While I have shown and described the pre- 1 ferred embodiment of my invention, I wish it to be understood that I do not confine myself 'to the precise details of constructionherein set forth, by way of illustration, as itis apparent that many changes and variations may be made therein, by those skilled in theart, without departing from the spirit of the invention, or exceeding the scope of the appended claims; A

I claim:

1. In a high frequency circuit, a vacuum tube having loss oscillating circuit of small inductance and large capacitance connected across said grid and plate, and a plurality of radio frequency choke coils connected between the filament and the grid on one side and the filament and plate on the other producing across said oscillating circuit a driving electromotive force.

2. A vacuum tube having a filament, grid and plate, a tank circuit comprising a low inductance, large capacltance and low lossesv connected across the grid and plate, a coil between the filament and grid and a second coil between the filament and plate of the tube. a

3. A vacuum tube having a filament, grid and plate a low loss tank circuit comprising a low inductance and large capacitance connected across the grid and plate, and means to produce high frequency oscillations in said tank circuit comprising two coils placed respectively between the filament and eachof the cold electrodes of the tube.

4. A vacuum tube having a filament, grid and plate, a low loss tank circuit comprising a low inductance and large capacitance connected across the grid and plate and means. to produce high frequency oscillation in the tank circuit comprising two coils placed respectively between the filament and each of the cold electrodes of the tube.

5. A vacuum tube having a filament, plate and grid, a low loss tank circuit comprising a low inductance and large capacitance connected across the grid and plate, and means to excite the tank circuit by high frequency voltage comprising two coils placed respectively and independently in the grid and plate circuits of the tube. 7 p V 6. A vacuum tube having a filament, grid and plate, a tank circuit comprising a low inductance and a large capacitance connected across the grid and plate, means to'excite the tank circuit by highfrequency voltage produced by the geometric sum of two electromotive forces comprising two coils placed respectively and independently in the grid and plate circuits of the tube.

A vacuum tube oscillator including a filament, grid and plate, a tank circuit connected between the plate and grid of the tube, and means to induce high frequency oscillations in the tank circuit by two electromotive forces substantially 180 out of'phase comprising two coils connecting respectively the filament and grid on one side andthe filament and plate on the other'side.

8. A vacuum tube oscillator including a a filament grid and plate, a low interelectrode capacities of the tube.

stant whenthe steady plate voltage-is varied nected across the grid and plate including a low inductance and high capacitance, a coil placedbetween the filament'andgrid'and'anfilament, plate and grid", a low lossztanklciri cuit connected between the grid and plate, and means to induce high. frequency oscillations in the tank circuits comprisingi'two coils placed respectively and independently in the grid and platecircuit of saidtube so as to produce a composite driving electromo tiveforce," and" in which the high frequency oscillations are renderedind'ependent ofsthe m 9. A vacuum. tubeoscillator comprising a filament, grid and plate, a tank circuit including a low. inductance: and large capac itance connected across the gridandthe plate, means toproduce high frequency oscillations in the tank circuitcomprising two coils: connected: respectively between the grid and .filament and between the plate and filament of the tube whereby. the "exciting independent electromotive forces generated in the grid and plate circuits maintain their frequency constant when-the filament temperature varies within the limits of the order: of25% of" the normal value. r

10.A vacuum tube oscillator-comprising afilament, grid and plate, a" tank circuit; including, a low inductance and large capacitance connected across the: grid and plate, means to produce high frequency oscillations in the tankcircuit comprising two coils respectively betweenthe grid and plate of the tube whereby the exciting independent electromotive forces'generated in the grid and plate'circuitsmaintain their frequency conwithin 50% of the normal value. 11. A vacuum' tube oscillator comprising a filament, grid and plate, a tank circuit conother coil" placed between the filament and plate of the tube whereby high frequency oscillations are produced inthe tankcircuit and are "rendered substantially independent of the length of the leads connecting the plate and grid to the tank circuit.

12. A vacuum tube oscillator comprising a filament, grid and plate, a tank circuit connected across the grid and plate including a low inductance and high capacitance, a coil connected between the filament and grid and another coil connectedbetween' the filament and plate of the tube whereby high frequency oscillations are produced in the tank circuit and are rendered independent of the lengths of the leads connecting the filament and plate circuit to the low and high tension batteries.

13. A constant frequency oscillator com-11:5 prising a grid circuit, a plate circuit and a, tank circuit having an inductance and a capacity connected between the grid and" plate circuits, the characteristics of the tank circuit being such as to render the stray capacitieswio ti ally negligible.

prising grid and plate circuits,

and plate circuits,

in the associated 'circuits substantially negligible. 1

14. A constant frequency oscillator coma tank circuit havingasmall inductance and large capacity'connected between the grid and plate circuits, the characteristics of the tank circuit being so chosen as to render stray capacities in the associated circuits substantially negligible. V

'15; In a tube having filament, grid, and plate, a low loss oscillating circuit of small inductance and large capacitance connected across said gridzand plate, and aplurality of radio frequency choke coils at least one of which is the filament and the grid,

connected between producing across said oscillating circuit a driving electromotive force.

16. In a hi h frequency circuit, a vacuum tube having lament, grid, and plate, a low loss oscillating circuit of small inductance and large'capacitanceconnected across said grid and plate, and a plurality of radio frequency choke coils, at least one of which is connected between the filament and the plate,

producing across said oscillating circuit a drivin electromotive force.

constant frequency oscillator comrisin a rid circuit a late circuit and a I a; a a

tank circuit having a fixed inductance anda variable capacity connected between the grid f the and plate circuits, the characteristics 0 tank circuit being such as to render the stray capacities in the associated circuits substan- 18. A constant frequency oscillator comprising grid and plate circuits, a tank circuit having a small fixed inductance and large variable capacity connected between the grid the characteristics of the tank circuit being so chosen as to render stray capacities in the associated circuits substantially negligible.

Intestimony whereof I ailix my signature.

I CONSTANTIN D. BARBULESOO;

high frequency circuit, a vacuum a 

